Wait a minute. Did you say [Ask the Rabbi Issue #123] "About
oinkers, the Torah prohibits eating the flesh only. The hoofs,
hair and bones (excluding the marrow), are permitted?????"
Hummmh. Isn't unkosher gelatin made from pigs' hooves? Then
why is it unkosher if it's kosher? I always thought nothing edible
about the pig was kosher. Please expand on this question.

Dear DanPatents@aol.com,

Gelatin is made from collagen, an animal protein. Collagen is
extracted from the skin/bones of cows or pigs. It's soaked and
cooked, then filtered, refined and evaporated. The finished product
is gelatin.

The Torah prohibits only the meat of unkosher animals, but not
the bones, horns or hoofs.

The Sages, however, forbade any bones, horns or hoofs which contain
moisture. According to this, food made from unkosher bones is
forbidden, unless the bones were completely dry.

But during the manufacturing of gelatin, the animal extract becomes
totally inedible, such that even a dog will no longer eat it.
Now, food which even a dog won't eat loses its status as food.
Halachically, it's no different than stones or dirt which are
you allowed to eat!

Based on this, some authorities permit gelatin from unkosher animals,
since during the process the animal extract becomes unfit for
even a dog. Rabbi Moshe Feinstein, zatzal, rules otherwise.
He writes that although the animal parts are inedible in the
middle of the process, this inedible state is only temporary.
Since at the end of the process the unkosher bones are 'resurrected'
into an edible product, the original prohibition remains.

In the United States, almost all kashrut organizations accept
the stricter opinion and do not endorse gelatin made from unkosher
derivatives.

Speaking of animal skins:
Little girl: Daddy, what is leather made of?
Daddy: Hide.
Little girl: What did you say?
Daddy: Hide, hide! The cow's outside.
Little girl: But, Daddy, I'm not afraid of the cow!

Sources:

Leviticus 11:9

Maimonides, Mishneh Torah, Laws of Prohibited Food 4:21

Tractate Temura 31

Rabbi Chaim Ozer Grodzinski, Responsa Achiezer vol. 3, 3:5

Rabbi Moshe Feinstein, Responsa Iggrot Moshe Yoreh De'ah 2:23

Olorin wrote:

What about the skin, can we eat the pig skin?

Dear Olorin:

Pig's skin which is dry and hard is permitted to be eaten. Therefore
if you check your pig-skin wallet and find no cash for food ...
you can eat the wallet!

Bob wrote:

Is gelatin from a kosher animal pareve?

Dear Bob,

During the process of making, the animal parts become inedible
and lose their status as meat. Also, they lose any taste of meat.
In theory, such gelatin would be pareve - meaning you
can eat it with milk. In practice, kosher gelatin is usually
made of agar-agar - a plant (seaweed) derivative.